<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #box{
      padding: 20px;
      background: palegoldenrod;
    }
  </style>
</head>
<body>
  <div id="box"></div>
  <button id="btn1">执行计算任务</button>
  <button id="btn2">更改背景颜色</button>
  <script>
    var box = document.getElementById('box')
    var btn1 = document.getElementById('btn1')
    var btn2 = document.getElementById('btn2')
    var number = 999999
    var value = 0
    function calc(deadline) {
      while(number > 0 && deadline.timeRemaining() > 1) {
        value = Math.random() < 0.5 ? Math.random() : Math.random()
        console.log(value)
        number --
      }

      requestIdleCallback(calc)
    }

    btn1.onclick = function() {
      requestIdleCallback(calc)
      // calc()
    }

    btn2.onclick = function () {
      box.style.background = "green"
      setTimeout(() => {
        box.style.background = "red"
      }, 1000)
    }
  </script>
</body>
</html>